A high-performance microprocessor has recently been developed, and a computer unit (ECU (Electronic Control Unit)) including a large number of microprocessors is incorporated in a vehicle such as an automobile. The ECU seeks driving performance, safety, comfort, resource-saving, energy-saving, and the like, and the ECU is incorporated in order to control a power train system, a body system, a safety system, an information system, and the like of the vehicle.
For example, each ECU controls: a vehicle motion system including an engine, a brake, a steering wheel, a suspension, and a transmission (the ECU may control a part of or all of these parts in an integrated manner); the body system including a power door, a power seat, an air conditioner, and a light; the safety system including an air bag and a collision sensor; and the information system including a car navigation device and a car audio apparatus.
On the other hand, in these ECUs, a program stored in advance is executed by a CPU (Central Processing Unit) within the ECU. A storage device stores the program itself, an operation result during execution of the program, an operation result after execution of the program, a map referred to in program execution, or the like (collectively denoted as “data”). Storage media such as a hard disk, a variety of ROMs (Read Only Memory), a variety of RAMs (Random Access Memory), or the like are used as the storage device. The hard disk, the ROM, and the RAM have a variety of characteristics respectively.
Japanese Patent Laying-Open No. 2000-251396 (document 1) discloses an on-vehicle information processing device including a writable hard disk and reliably carrying out writing in the hard disk. The on-vehicle information processing device with the hard disk includes a semiconductor memory capable of recording information to be written in the hard disk, a failure sensing unit sensing a state that may cause failure in a operation to write in the hard disk, and a control unit writing information to be written in the hard disk into the semiconductor memory when the state that may cause failure is sensed by the failure sensing unit and writing the information written in the semiconductor memory into the hard disk when the state that may cause failure is no longer sensed.
According to the on-vehicle information processing device, the failure sensing unit monitors a state of the hard disk. When a state that may cause failure in data writing is present, information to be written is once stored in the semiconductor memory. When such a state is no longer present, data writing to the hard disk is reliably carried out.
Japanese Patent Laying-Open No. 2001-075873 (document 2) discloses a method of data back-up attaining high cost-effectiveness. The data back-up method of saving data in a multi-platform environment includes the steps of: managing a significance level of each data as well as a reliability level or a speed of a back-up storage device; and saving each data in an optimal back-up storage device.
According to the data back-up method, the significance level of the data in the multi-platform environment as well as the reliability level or the speed of the back-up storage device are managed so as to optimize a back-up target. As a result, back-up attaining high cost-effectiveness can be carried out.
The ECU, the hard disk and the like incorporated in a vehicle are supplied with electric power from a battery incorporated in the vehicle. A semiconductor memory such as an ROM or an RAM is implemented within the ECU. The storage medium such as the hard disk or the semiconductor memory has such a characteristic as inability to hold data when power supply is turned off as in a semiconductor memory called a volatile memory, or a characteristic as ability to hold data even when the power supply is turned off as in a semiconductor memory called a non-volatile memory or a hard disk. Power supply to these storage media is controlled based on a state of an ignition switch of a vehicle, a state of a system main relay (SMR), or the like. In addition, reliability in data storage (whether or not a state in which data is correctly stored can be held) is different between the semiconductor memory and the hard disk, for example.
Meanwhile, the data stored in such a storage medium has different significance depending on a type thereof. For example, data for realizing control determined by a regulation concerning the vehicle, data on security, or data related to safety has highest significance. On the other hand, for example, a learning control parameter while learning control is exerted for optimal control of an engine or a transmission is overwritten every sampling time. Accordingly, significance of the learning control parameter is lower than that of the data described above. In this manner, the data to be stored has different significance for each type.
As described above, a plurality of types of storage media having a variety of storage characteristics are incorporated in a vehicle, whereas the data to be stored has different significance. Therefore, in view of the significance of the data in particular, preferably, the storage media are used, with definite distinction being drawn among them with respect to data reliability and a data holding period. Though it is possible to store all data only in a storage medium attaining high reliability and having a data holding period independent of a power supply state, this will cause cost increase. In view of the foregoing, problems in the documents set forth above will be discussed.
The on-vehicle information processing device disclosed in document 1 is not paying attention to the data significance. Instead, this device simply stores the data in a non-volatile memory when a state that may cause failure in the operation to write in the hard disk is sensed. If many states that may cause failure in the writing operation are assumed, a non-volatile memory capable of storing all data to be stored in the hard disk should be prepared, which may result in a larger size of the storage device and cost increase.
According to the data back-up method disclosed in document 2, a server system simply has a setting of a significance level with respect to storage at each platform, so that a back-up target is optimized in accordance with the setting. That is, the data of high significance is stored in a highly reliable storage device, while data of low significance is stored in a less reliable storage device. According to the disclosure, a tape library device is adopted as a first storage device having the highest reliability level, a magnetic disk device is adopted as a second storage device having a second highest reliability level, and a magnetic disk device is adopted as a third storage device having a third highest reliability level. With this method, only one storage medium for storing the data can be selected from these storage devices in an alternative manner.
A further problem will be discussed from a point of view different from these documents. Conventionally, a storage medium in which the data is to be stored has been designated in a program. Accordingly, it has been necessary to designate a storage medium to store that data based on significance of the program among a large number of programs to be executed in a vehicle and on significance of the data in the program. When a new and highly reliable storage medium is mounted as a result of modification of a hardware configuration in a vehicle control system or when a method of attaining redundancy is modified, however, a program (application software) should be modified. In that case, since total review of a large number of programs may be necessary, productivity of the application software is considerably lowered.